JP2005308825A - Display element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a display element comprising a dielectric medium which does not cause lowering of Kerr effect and of which the phase transition temperature between a liquid crystal phase and an isotropic phase is not high. <P>SOLUTION: The display element is equipped with a pair of substrates 1, 2, of which at least one is transparent, the dielectric medium interposed between the pair of substrates 1, 2, of which the optical anisotropy varies with application of an electric field, and at least a pair of electric field applying means 4, 5 which applies the electric field nearly parallel to at least one out of the pair of substrates 1, 2 to the dielectric medium, wherein non-polar molecules are contained in the dielectric medium. Since the non-polar molecules are comparatively little influenced by dipole interaction etc. in a molecular aggregate of the dielectric medium, alignment of the dielectric medium is easily changed owing to inclusion of the non-polar molecules in it. As a result, heightening of voltage required for the optical modulation is suppressed. Consequently, owing to the inclusion of the non-polar molecules in the dielectric medium, differently from an optical element (an optical device) in the conventional technique, the heightening of the voltage required for the optical modulation is suppressed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a display element, and more particularly, to a display element having a high-speed response and a wide-field display performance.

  Currently, a variety of display elements are known. Among them, liquid crystal display elements are thin, lightweight, and low power consumption display elements, such as image display devices such as televisions and videos, monitors, word processors, personal computers, etc. It is widely used in OA (Office Automation) equipment.

  Conventionally, a twisted nematic (TN) mode liquid crystal display element using a nematic liquid crystal has been put into practical use. However, this TN mode liquid crystal display device has the disadvantages that the response speed is slow and the viewing angle is narrow.

  Furthermore, display modes such as a ferroelectric liquid crystal (FLC) or an antiferroelectric liquid crystal (AFLC) are also known, and these have the characteristics that the response speed is high and the viewing angle is wide. However, these display modes have major drawbacks in shock resistance, temperature characteristics, etc., and have not yet been widely put into practical use.

  Further, it is known that a polymer dispersion type liquid crystal display element using light scattering does not require a polarizing plate and can display with high luminance. However, this polymer-dispersed liquid crystal display element has a problem in terms of response characteristics of image display, and cannot be said to be a liquid crystal display element superior to the above-described TN mode liquid crystal display element.

  The various display elements (liquid crystal display elements) described above are display mechanisms that use the rotation of molecules by applying an electric field, but recently, different display mechanisms have been proposed. Specifically, it is a display element using a substance whose optical anisotropy changes when an electric field is applied, in particular, a substance showing orientation polarization or electronic polarization due to an electro-optic effect. The electro-optic effect refers to a phenomenon in which the refractive index of a substance is changed by an external electric field. In addition, the electro-optic effect has an effect in which the refractive index of the substance is proportional to the primary of the electric field and an effect in which the refractive index of the substance is proportional to the secondary of the electric field. Yes.

  Substances exhibiting the Kerr effect have been applied to high-speed optical shutters from an early stage. Therefore, it has been put into practical use for special measuring instruments. The Kerr effect was discovered by J. Kerr in 1875, and the refractive index of a substance exhibiting the Kerr effect is proportional to the second order of the applied electric field. Therefore, when a material exhibiting the Kerr effect is used for orientation polarization, a lower voltage drive can be expected than when a material exhibiting the Pockels effect is used for orientation polarization. Furthermore, since a substance exhibiting the Kerr effect exhibits a response characteristic of several microseconds to several milliseconds, it is expected to be used to cause a display by a display device to respond to an input voltage at high speed.

  Conventionally, nitrobenzene, carbon disulfide, and the like are known as materials exhibiting the Kerr effect, and these materials are used for, for example, high electric field strength measurement of power cables and the like in addition to the optical shutter described above. . It was used to measure high electric field strength in power cables and the like. Later, it was discovered that liquid crystal materials also exhibit the Kerr effect, and basic studies for application to optical modulation elements, optical polarization elements, and optical integrated circuits were conducted. Liquid crystal compounds exhibiting a Kerr constant exceeding 200 times that of nitrobenzene have also been reported.

  Under such circumstances, application to a display element (liquid crystal display device) having a secondary electro-optic effect (hereinafter referred to as Kerr effect) has begun to be studied. As a problem in the application development to the Kerr effect display element, the Kerr effect display element has a high driving voltage and a high liquid crystal phase-isotropic phase transition temperature.

Therefore, Patent Document 1 discloses a display device using the Kerr effect. This display device is a display device that reduces the liquid crystal phase-isotropic phase transition temperature by adding polar molecules such as ethyl alcohol to the liquid crystal material.
JP 2001-249363 A (publication date: September 14, 2001) Shiro Matsumoto, 3 others, “Fine droplets of liquid crystals in a transparent polymer and their response to an electric field”, Appl. Phys. Lett., August 1996, vol. 69. No. 8, p. 1044-1046 Takashi Kato and two others, “Fast and High-Contrast Electro-optical Switching of Liquid-Crystalline Physical Gels: Formation of Oriented Microphase-Separated Structures”, Adv. Funct. Mater., April 2003, vol. 13. No. 4, p313-317 Kazuya Saito, 1 other person, “Thermodynamics of unusual thermotropic liquid crystals that are optically isotropic”, Liquid Crystals, 2001, Vol. 5, No. 1. p.20-27 Jun Yamamoto, “Liquid Crystal Microemulsion”, Liquid Crystal, 2000, Vol. 3, No. 3, p.248-254 Yukihide Shiraishi, 4 others, “Palladium nanoparticles protected with liquid crystal molecules—Preparation and application to guest-host mode liquid crystal display devices”, Polymer Papers, December 2002, Vol. 59, No. 12, p. .753-759 Hirotsugu kikuchi, 4 others, "Polymer-stabilized liquid crystal blue phases", p. 64-68, [online], September 2, 2002, Nature Materials, vol. 1, [Search July 10, 2003], Internet <URL: http://www.nature.com/naturematerials> Makoto Yoneya, “Searching for Nanostructured Liquid Crystal Phases by Molecular Simulation”, Liquid Crystals, 2003, Vol. 7, No. 3, p.238-245 D. Demus, 3 others, "Handbook of Liquid Crystals Low Molecular Weight Liquid Crystal", Wiley-VCH, 1998, vol. 2B, p. 887-900 D. Demus, 3 others, "Handbook of Liquid Crystals Low Molecular Weight Liquid Crystal", Wiley-VCH, 1998, vol. 1, p. 484-485 Eric Grelet, 3 others, “Structural Investigations on Smectic Blue Phases”, PHYSICAL REVIEW LETTERS, The American Physical Society, April 23, 2001, vol. 86, no. 17, p3791-3794 Jun Yamamoto, "Liquid Crystal Science Laboratory 1st: Identification of Liquid Crystal Phase: (4) Lyotropic Liquid Crystal", Liquid Crystal, 2002, Vol. 6, No. 1, p.72-83 Junichi Yamamoto, 1 outside, “Organic electro-optic material”, National Technical Report, December 1976, vol. 22, no. 6, p. 826-834

  Patent Document 1 is a display device in which a medium including a polar molecule in an isotropic phase is sandwiched between a pair of substrates, and is a display device using the Kerr effect. This display device does not switch light transmission and blocking according to the movement of molecules in the conventional liquid crystal display device, but displays images by switching light transmission and blocking by electron bias.

  However, the display device disclosed in Patent Document 1 is an effective method only for reducing the liquid crystal phase-isotropic phase transition temperature among the problems mentioned above as a display device using the Kerr effect. is there. In other words, the liquid crystal phase-isotropic phase transition temperature can be lowered, but the liquid crystal phase-isotropic phase transition temperature is lowered, and at the same time, the Kerr constant is lowered, thereby increasing the drive voltage. Has the problem of causing.

  Accordingly, the present invention has been made in view of the above-described problems, and an object of the present invention is to provide a display made of a dielectric medium that does not cause a decrease in the Kerr effect and does not have a high liquid crystal phase-isotropic phase transition temperature. It is to provide an element.

  In order to solve the above-described problem, a display element according to the present invention is a dielectric that is sandwiched between a pair of substrates at least one of which is transparent and the optical anisotropy is changed by applying an electric field. The dielectric medium includes a nonpolar molecule. The display element includes a medium.

  By adopting the above-described configuration, even if the display element according to the present invention is a display element using the Kerr effect, the problems as described above in the prior art can be solved. That is, the display element according to the present invention can provide a display element that does not have a high liquid crystal phase-isotropic phase transition temperature and that suppresses an increase in drive voltage necessary for optical modulation.

  Specifically, the display element according to the present invention includes a nonpolar molecule in the dielectric medium. Nonpolar molecules are less susceptible to effects such as dipole interactions in a molecular assembly in a dielectric medium and are therefore subject to orientation changes. For this reason, it is considered that an increase in voltage necessary for optical modulation can be suppressed.

  That is, the display element according to the present invention can perform optical modulation while suppressing an increase in driving voltage, and has a high-speed response characteristic capable of reducing the liquid crystal phase-isotropic phase transition temperature. Can be provided.

  The display element according to the present invention further includes an electric field applying means for applying an electric field to the dielectric medium, and at least one of the pair of substrates on a side opposite to the surface facing the dielectric medium. It is preferable that a polarizing plate is provided.

  With the above-described configuration, the display element according to the present invention can modulate the transmittance by applying an electric field to the dielectric medium to develop birefringence.

  In the display element according to the present invention, the dielectric medium may exhibit optical isotropy when no electric field is applied, and exhibit optical anisotropy when a voltage is applied. The optical anisotropy may be exhibited by applying a voltage.

  In any of the above configurations, by applying an electric field, the shape of the refractive index ellipsoid of the dielectric medium can be changed between when no electric field is applied and when an electric field is applied, and the direction of optical anisotropy is constant. The display can be performed by changing the degree of optical anisotropy (degree of orientation order, refractive index). Therefore, in any of the above configurations, a display element having a wide viewing angle characteristic and a high-speed response characteristic can be realized.

  In the display element according to the present invention, it is preferable that the dielectric medium has an alignment order equal to or less than the wavelength of light when a voltage is applied or no voltage is applied.

  Thus, if the orientation order is equal to or less than the wavelength of light, it is optically isotropic. Therefore, by using a medium whose alignment order is equal to or less than the wavelength of light when a voltage is applied or when no voltage is applied, the display state can be reliably changed between when no voltage is applied and when a voltage is applied.

  The display element according to the present invention further includes an electric field applying unit including at least one pair of electrodes for applying an electric field substantially parallel to the substrate surface to the dielectric medium on one of the pair of substrates. Preferably it is.

  With the above-described configuration, an electric field can be easily applied in a direction substantially orthogonal to light passing in a direction perpendicular to the substrate, that is, a direction parallel to the substrate surface, and is generated by application of the electric field. Birefringence anisotropy can be easily extracted as a change in the optical signal.

  In the display element according to the present invention, the electrode is more preferably wedge-shaped, and the angle formed by the electrode formed in the wedge-shape is preferably less than 90 ± 10 degrees.

  With the above-described configuration, the viewing angle characteristics of the display element according to the present invention are improved.

  In the display element according to the present invention, the angle formed by the electric field application direction by the electric field application unit and the absorption axis of the polarizing plate is preferably less than 45 ° ± 10 °.

  There are at least two directions (two domains) of the optical anisotropy direction of the dielectric medium generated by the electric field application by the electric field application means formed in the wedge shape having a degree of less than 90 ° ± 10 °. become. The angle between the direction of optical anisotropy generated by applying an electric field in each domain and the absorption axis of the polarizing plate is less than 45 ° ± 10 °, and the optical difference generated by applying an electric field in each domain. When the directions of the directions are less than 90 ° ± 10 °, the coloring phenomenon of the oblique viewing angle can be compensated for each other, and the viewing angle characteristics can be greatly improved without impairing the transmittance.

  In the display element according to the present invention, an alignment film is preferably provided on the surface of at least one of the pair of substrates facing the other substrate, and a horizontal alignment process is performed. Is preferred.

  By performing the alignment treatment, the degree of alignment order of the liquid crystal can be improved, and a larger Kerr effect can be obtained.

  That is, for example, when the ambient temperature is low, when the power is turned on, the dielectric medium does not reach the temperature to be driven originally, and the physical state of the dielectric medium is different from the original driving state. Even so, since the dielectric medium can be oriented, the optical contribution of the dielectric medium (dielectric medium whose physical state is different from the original driving state) can be eliminated.

  Therefore, the display device according to the present invention can assist the change in the orientation of the dielectric medium, and contribute to the increase of the Kerr effect by assisting the change in the orientation of the dielectric medium. It becomes possible to reduce.

  Further, by performing the above-described processing, it is possible to realize a good display even until the temperature of the display element rises.

  Further, according to the above configuration, even when the desired driving temperature is reached, light leakage due to molecules of the dielectric medium adsorbed on the substrate interface does not occur, and high contrast can be obtained. Therefore, according to said structure, there exists a further effect that a display element excellent in high-speed responsiveness and a viewing angle characteristic can be provided, without a contrast falling.

  In the display element according to the present invention, the alignment film is preferably an organic thin film, and more preferably a polyimide film.

  By using an organic thin film, particularly polyimide, as the alignment film, an extremely excellent alignment effect can be exhibited. That is, the Kerr constant can be easily increased. The polyimide is a highly stable material and has high reliability. Therefore, the display element which shows favorable display performance can be provided by using a polyimide.

  In the display element according to the present invention, the dielectric medium preferably contains a liquid crystalline substance.

  By applying an electric field to the liquid crystalline substance, the fine structure is distorted and optical modulation can be induced.

  As described above, the display element according to the present invention includes a pair of substrates, at least one of which is transparent, and a dielectric medium which is sandwiched between the pair of substrates and whose optical anisotropy changes when an electric field is applied. Since the display medium is characterized in that the dielectric medium contains nonpolar molecules, even the display element using the Kerr effect can solve the above-described problems in the prior art. That is, since the display element according to the present invention includes nonpolar molecules in the dielectric medium, the nonpolar molecules are relatively less susceptible to dipole interaction or the like in the molecular assembly in the dielectric medium. Therefore, the orientation change is likely to occur. Therefore, an increase in voltage necessary for optical modulation can be suppressed. Therefore, it is considered that the increase in voltage necessary for optical modulation can be suppressed by including nonpolar molecules in the dielectric medium, unlike the optical element (optical device) in the prior art.

  Further, with the above structure, even when the liquid crystal material is applied to a display element in an isotropic phase state by heating with a heater that is a phase transition unit, the Kerr constant does not decrease, and the liquid crystal material does not decrease. The isotropic phase transition temperature can be lowered. Since the Kerr constant does not decrease, a display element including a liquid crystal material that can be driven at a low voltage without increasing the applied voltage can be realized.

  Furthermore, since the heating temperature by a heater etc. can be reduced, the display element provided with the wide use temperature range compared with the past can be provided.

  Therefore, the display element according to the present invention can provide a display element having a high-speed response characteristic capable of reducing the temperature at which optical modulation is performed while suppressing an increase in drive voltage. That is, the display element according to the present invention can provide a display element that does not have a high liquid crystal phase-isotropic phase transition and suppresses an increase in drive voltage necessary for optical modulation.

  An embodiment of the present invention will be described with reference to FIGS. 1 to 8 as follows. However, the present invention is not limited to this.

  FIG. 1A is a cross-sectional view schematically showing a schematic configuration of a main part of the display element according to the present embodiment in a voltage non-application state (OFF state), and FIG. It is sectional drawing which shows typically schematic structure of the principal part of the display element which concerns on this Embodiment in an ON state.

  As shown in FIGS. 1A and 1B, the display element according to the present embodiment includes a pair of substrates (hereinafter referred to as a pixel substrate 11 and a counter substrate 12) that are arranged to face each other and at least one of them is transparent. And a dielectric medium layer 3 made of a dielectric medium optically modulated by application of an electric field is sandwiched between the pair of substrates, and one of the pair of substrates (in the figure) Then, the pixel substrate 11) is provided with electrodes 4 and 5 as electric field applying means, and further with polarizing plates 6 and 7.

  The pixel substrate 11 and the counter substrate 12 have substrates 1 and 2, respectively, as shown in FIGS. 1 (a) and 1 (b). Further, polarizing plates 6 and 7 are provided on the outside of the pair of substrates 1 and 2 (outside of the pixel substrate 11 and the counter substrate 12), that is, on the surface opposite to the opposing surface of the substrates 1 and 2, respectively. It has the structure provided.

  Of the pair of substrates 1 and 2, at least one of the substrates may be a light-transmitting substrate such as a glass substrate.

  The substrates 1 and 2 are not limited to those conventionally used as substrates. For example, the substrates 1 and 2 may be in the form of a film or may be flexible. If one side is transparent and the dielectric medium can be held (clamped) between substrates, that is, inside, various materials are used depending on the type of dielectric medium and the state of the phase. can do.

  Of the pair of substrates 1 and 2, on the surface of one substrate 1 facing the other substrate 2, the dielectric medium layer 3 is formed on the substrate 1 as shown in FIGS. Electrodes 4 and 5 for applying to are arranged opposite to each other. As shown in FIG. 1B, in the voltage application state, the electrodes 4 and 5 apply a substantially parallel electric field 8 in the dielectric medium. Here, “an electric field substantially parallel to the substrate 1” means an electric field in a direction substantially orthogonal to light passing in a direction perpendicular to the substrate.

  The electrodes 4 and 5 are made of an electrode material such as a transparent electrode material such as ITO (indium tin oxide). In the present embodiment, for example, the line width is 5 μm, the distance between electrodes (electrode interval) is 5 μm, and the thickness is 0. It is set to 6 μm. However, the above electrode material, line width, interelectrode distance, and thickness are merely examples, and the present invention is not limited thereto.

  An example of the electrodes 4 and 5 is a comb-shaped electrode in which the comb-tooth portions 4a and 5a are arranged to face each other as shown in FIG. Furthermore, it is preferable that each of the comb-tooth portions 4a and 5a has a wedge shape. Specifically, as shown in the figure, each of the comb portions 4a and 5a may be bent in a zigzag shape. For example, when a data signal line and a scanning signal line are provided in each column and each row of a plurality of pixels arranged in a matrix by being bent in a zigzag shape, the comb-tooth portion of the electrode and the data The non-display area generated between the signal line and the scanning signal line can be greatly reduced, and the display area can be enlarged.

  However, the electrodes 4 and 5 are not particularly limited as long as an electric field 8 substantially parallel to the substrate 1 can be applied to the dielectric medium layer 3. The wedge shape refers to a structure that is refracted into a "<" shape.

  Further, the electrodes 4 and 5 formed in the wedge shape are each refracted at an angle of 90 degrees ± 10 degrees, more preferably less than 90 degrees ± 5 degrees, and most preferably 90 degrees. It is preferable.

  The direction of the optical anisotropy of the dielectric medium generated by the application of an electric field by the electrodes 4 and 5 having the above-mentioned angles is at least two directions (hereinafter referred to as the arrows 50a and b shown in FIG. 2). (Referred to as two domains). Therefore, as will be described later, the angle formed by the absorption axis of the polarizing plate is 45 degrees, and the directions of optical anisotropy generated by the application of the electric field in each domain are 90 degrees to each other. Can be compensated for each other, and the viewing angle characteristic can be greatly improved without impairing the transmittance.

  Further, a rubbing alignment film 9 covers the electrodes 4 and 5 on the surface of the substrate 1 facing the substrate 2, that is, on the surface of the pixel substrate 11 facing the counter substrate 12. Thus, it is formed over the entire surface of the substrate 1 facing the substrate 2.

  Further, the alignment film 10 that has been subjected to the rubbing process on the surface of the substrate 2 facing the substrate 1, that is, the surface of the counter substrate 12 facing the pixel substrate 11, Is formed over the entire surface of the opposite surface.

  As shown in FIG. 2, the alignment films 9 and 10 are rubbed so that the rubbing direction thereof coincides with one of the absorption axes 6a and 7a of the polarizing plates 6 and 7. As processing, horizontal rubbing processing (horizontal alignment processing) in which the alignment processing direction is the in-plane direction of the substrate is performed. By performing the alignment treatment, the degree of alignment order of the liquid crystal can be improved, and a larger Kerr effect can be obtained.

  Further, as shown in FIGS. 2 and 1, the polarizing plates 6 and 7 are arranged so that the polarizing plate absorption axis directions thereof are orthogonal to each other, and the polarizing plate absorption axis in each polarizing plate 6 and 7 is: An angle of 45 degrees is formed with respect to the electric field application direction of the electrodes 4 and 5.

In the display element according to the present embodiment, the dielectric medium layer 3 functions as a shutter-type display element that exhibits optical anisotropy due to an increase in the degree of orientational order in the direction of electric field application and the transmittance changes. Can do. Therefore, with respect to the polarizing plate absorption axis directions orthogonal to each other, the anisotropic direction gives the maximum transmittance when forming an angle of 45 degrees. Note that the transmittance (P) when the orientation in which the optical anisotropy of the dielectric medium appears exists at an angle of ± θ (degrees) with respect to the polarizing plate absorption axis is P (%) = sin ^2. Since it is estimated from (2θ) and the transmittance when the θ is 45 degrees is 100%, it is felt that the human eye has the maximum luminance when the transmittance is approximately 90% or more. If the above θ is 35 degrees <θ <55 degrees, it is felt that the human eye has the maximum luminance. That is, as shown in the present embodiment, in a display element in which an electric field is applied, for example, substantially parallel to the substrate 1, the direction of the absorption axis of the polarizing plate, in other words, the alignment treatment direction (rubbing direction) in the horizontal alignment treatment. The transmittance is maximized by forming an angle of less than 45 ° ± 10 °, more preferably less than 45 ° ± 5 °, and most preferably 45 ° with respect to the direction of electric field application by the electrodes 4 and 5. be able to.

  Next, the polarizing plates 6 and 7 are provided on both the substrates 1 and 2, respectively, and the polarizing plate absorption axis directions of the polarizing plates 6 and 7 are orthogonal to the polarizing plate absorption axes of the respective polarizing plates 6 and 7. The comb-teeth portions 4a and 5a) are formed so as to form an angle of 45 degrees with the electrode extending direction.

  Therefore, in the display element, the electric field application direction by the electrodes 4 and 5 forms an angle of 45 degrees with the absorption axis direction of the polarizing plates 6 and 7 and the rubbing direction of the alignment films 9 and 10. Yes.

  As long as the rubbing directions in the alignment films 9 and 10 coincide with the polarizing plate absorption axis of any one of the polarizing plates 6 and 7 as described above, they are parallel to each other. May be parallel and in the same direction), anti-parallel (anti-parallel), that is, the orientation (treatment) directions of each other may be parallel and opposite (reverse), and orthogonal Also good.

  That is, according to the present embodiment, even if optical anisotropy is manifested when no voltage is applied, the opposing surfaces of the pixel substrate 11 and the counter substrate 12 are parallel or orthogonal to one polarizing plate absorption axis. The optical contribution can be eliminated by applying a horizontal alignment treatment in the direction to be performed and keeping the direction of optical anisotropy, that is, the alignment direction parallel or orthogonal to the polarizing plate absorption axis. . In other words, in the present embodiment, the surfaces of the pixel substrate 11 and the counter substrate 12 facing each other are subjected to a horizontal alignment process, so that the dielectric medium at the substrate interface, strictly speaking, the dielectric medium is configured. The molecules to be aligned are aligned along the alignment (processing) direction in the alignment process at a temperature lower than the element driving temperature.

  In addition, according to the display element according to the present embodiment, even when the desired driving temperature range is reached, light leakage during black display due to molecules adsorbed on the substrate interface is not observed, and high contrast is realized. Can do. Therefore, it is possible to obtain a display element that is excellent in high-speed response and viewing angle characteristics without lowering the contrast.

  As described above, the rubbing directions of the substrates 1 and 2 are preferably orthogonal, parallel or antiparallel, but more preferably parallel or antiparallel. Contrast can be maximized by performing horizontal alignment treatment on both the substrates 1 and 2 and making the horizontal alignment directions parallel or anti-parallel to each other. As a result, the black luminance can be further reduced. It was.

  In this embodiment, the alignment films 9 and 10 are formed and the rubbing process is performed on both the substrates 1 and 2 (the pixel substrate 11 and the counter substrate 12). Even when the rubbing process is performed on the surface, it can be obtained. In this case, when the alignment films 9 and 10 are formed on both the substrates 1 and 2, that is, the effect is not as good as when the alignment treatment is performed on both the substrates 1 and 2, the electrodes 4 and 5 are formed. If the alignment film (alignment film 10) is formed only on the substrate 2 on the side opposite to the substrate 1, a voltage drop derived from the alignment film 9 on the substrate 1 side does not occur, and the drive voltage of the element increases. There are no practical advantages. Further, even if the driving temperature is reached, light leakage due to molecules adsorbed on the substrate interface does not occur, and high contrast can be obtained. Further, even if the driving temperature is reached, light leakage due to molecules adsorbed on the substrate interface does not occur, and high contrast can be obtained.

  The material of the alignment films 9 and 10 may be an organic film or an inorganic film, respectively, improve the degree of order of the molecules constituting the dielectric medium, The alignment film 9 and 10 is not particularly limited as long as it can be aligned in a desired direction, but when the alignment films 9 and 10 are formed of an organic thin film, the alignment film 9 and 10 10 is more preferably an organic thin film. Among such organic thin films, polyimide has high stability and reliability, and exhibits an extremely excellent alignment effect. Therefore, by using polyimide as an alignment film material, a display element having better display performance is provided. be able to.

  As the alignment films 9 and 10, commercially available horizontal alignment films can be used.

  The alignment films 9 and 10 may have a functional group having photosensitivity (hereinafter referred to as a photofunctional group) because the alignment control is easy. Examples of the photofunctional group include a cinnamate system and a chalcone system that perform a dimerization reaction, and an azo system that performs an isomerization reaction, but the present invention is not limited thereto.

  When the alignment films 9 and 10 have a photofunctional group, the surfaces of the pixel substrate 11 and the counter substrate 12, that is, the surfaces of the alignment films 9 and 10 are irradiated with polarized ultraviolet rays (hereinafter referred to as polarized ultraviolet light irradiation). ) To develop the alignment regulating force, the desired alignment treatment can be easily performed.

  In the display element according to the present embodiment, for example, the pixel substrate 11 and the counter substrate 12 are bonded to each other with a sealing agent (not shown) through a spacer such as a plastic bead or a glass fiber spacer (not shown) as necessary. The dielectric medium is sealed in the gap.

The dielectric medium of the dielectric medium layer 3 used in the present embodiment is a medium whose optical anisotropy changes when an electric field is applied. When an electric field E _j is applied to the material from the outside, an electric displacement D _ij = ε _ij · E _j is generated, and at that time, a slight change is also seen in the dielectric constant (ε _ij ). Since the square of the refractive index (n) is equivalent to the dielectric constant at the frequency of light, the dielectric medium can also be said to be a substance whose refractive index changes when an electric field is applied.

  As described above, the display element according to this embodiment performs display using a phenomenon (electro-optic effect) in which the refractive index of a substance is changed by an external electric field. Unlike liquid crystal display elements that utilize the fact that they rotate together, the direction of optical anisotropy hardly changes, and the degree of optical anisotropy changes (mainly electronic polarization and orientation polarization). Is displayed.

  The dielectric medium is optically isotropic when a field is not applied, such as a substance exhibiting a Pockels effect or a Kerr effect, and may be optically anisotropic by applying a field. It may be a substance that exhibits optical properties, has optical anisotropy when no electric field is applied, disappears when applied with an electric field, and is optically isotropic (being isotropic when viewed macroscopically) It is also possible to use a substance that shows Typically, a dielectric medium is optically isotropic when it is not applied with an electric field (it only needs to be isotropic when viewed macroscopically), and optically modulated by application of an electric field (especially birefringence increases by application of an electric field). It is desirable that the substance develops.

  The Pockels effect and the Kerr effect (which are themselves observed in the isotropic phase state) are electro-optic effects that are proportional to the primary or secondary electric field, respectively, and are in the isotropic phase when no voltage is applied. Although optically isotropic, in the voltage application state, in the region where an electric field is applied, the long axis direction of the compound molecules is oriented in the electric field direction, and birefringence is expressed, thereby modulating the transmittance. be able to. For example, in the case of a display method using a substance exhibiting the Kerr effect, by controlling the bias of electrons within one molecule by applying an electric field, each randomly arranged individual molecule rotates and becomes oriented. Is advantageous in that the response speed is very fast and the molecules are arranged randomly, and there is no viewing angle limitation. Note that among the above-mentioned dielectric media, those roughly proportional to the primary or secondary of the electric field can be treated as a substance exhibiting the Pockels effect or the Kerr effect.

  Examples of the substance exhibiting the Pockels effect include, but are not limited to, organic solid materials such as hexamine. As the medium A, various organic materials and inorganic materials exhibiting the Pockels effect can be used.

  Next, substances that exhibit the Kerr effect will be described as follows. That is, a substance exhibiting the Kerr effect is an electro-optic effect that is proportional to the second order of the electric field as described above, and is optically isotropic because it is isotropic when no voltage is applied. In the state, in the region where the electric field is applied, the long axis direction of the compound molecules is oriented in the electric field direction, and birefringence is expressed, whereby the transmittance can be modulated. By using a substance exhibiting the Kerr effect, by applying an electric field to control the bias of electrons within one molecule, each randomly arranged individual molecule rotates and changes its orientation, Since the response speed is very fast and the molecules are arranged randomly, there is an advantage that there is no viewing angle limitation.

  As a substance showing the Kerr effect, the following structural formulas (1) to (4)

And the following structural formulas (5) to (7) used in the examples described later,

Although the liquid crystalline substance shown by these is mentioned, it does not specifically limit.

  The Kerr effect is observed in a medium transparent to incident light. For this reason, the substance showing the Kerr effect is used as a transparent medium. Usually, a liquid crystalline substance shifts from a liquid crystal phase having a short-range order to an isotropic phase having random orientation at a molecular level as the temperature rises. In other words, the Kerr effect of liquid crystalline substances is not a nematic phase, but a phenomenon seen in liquids in the isotropic phase state above the liquid crystal phase-isotropic phase temperature. The liquid crystalline substances are used as transparent dielectric liquids. Is done.

  A dielectric liquid such as a liquid crystal substance is in an isotropic phase state as the use environment temperature (heating temperature) by heating is higher. Therefore, when a dielectric liquid such as a liquid crystal substance is used as the medium, in order to use the dielectric liquid in a liquid state that is transparent, that is, transparent to visible light, for example, (1) Dielectric A heating means such as a heater (not shown) may be provided around the medium layer 3, and the dielectric liquid may be heated to the clearing point or higher by the heating means, or (2) thermal radiation from the backlight or The dielectric liquid may be used by heating it above its clearing point by heat conduction from the backlight and / or peripheral drive circuit (in this case, the backlight or peripheral drive circuit functions as a heating means). Good. (3) A sheet heater (heating means) may be bonded to at least one of the substrates 1 and 2 as a heater and heated to a predetermined temperature. Furthermore, in order to use the dielectric liquid in a transparent state, it is possible to use a material having a clearing point lower than the lower limit of the operating temperature range of the display element.

  The dielectric medium preferably contains a liquid crystalline substance. When the liquid crystalline substance is used, the liquid crystalline substance is a transparent liquid that shows an isotropic phase macroscopically. Microscopically, it is desirable to include a cluster which is a molecular group having short-range order arranged in a certain direction. Since the liquid crystalline substance is used in a state transparent to visible light, the cluster is also used in a state transparent (optically isotropic) to visible light.

  For this purpose, as described above, the display element may be temperature-controlled using a heating means such as a heater, and the liquid crystal substance has a diameter of 0.1 μm or less, for example. Is a liquid crystal compound that is made into a transparent state by suppressing light scattering and having a transparent isotropic phase at the use environment temperature (room temperature). May be used. Light scattering can be ignored when the diameter of the liquid crystalline substance, and further, the diameter (major axis) of the cluster is 0.1 μm or less, that is, smaller than the wavelength of light (incident light wavelength). Therefore, for example, if the diameter of the cluster is 0.1 μm or less, the cluster is also transparent to visible light.

  Note that the dielectric medium is not limited to a substance exhibiting the Pockels effect or the Kerr effect as described above. For this reason, the dielectric medium has an ordered structure in which the molecular arrangement has cubic symmetry with a scale below the wavelength of light (for example, nanoscale), and is optically isotropic. (See Patent Documents 3 and 6 to 8). The cubic phase is one of the liquid crystal phases of the liquid crystalline substance that can be used as the dielectric medium. Examples of the liquid crystalline substance exhibiting the cubic phase include the following structural formula (8)

BABH8 etc. which are shown by these. When an electric field is applied to such a liquid crystalline substance, the fine structure is distorted and optical modulation can be induced.

  BABH8 shows a cubic phase composed of an ordered structure having cubic symmetry of a scale below the wavelength of light in a temperature range of 136.7 ° C. or more and 161 ° C. or less. The BABH 8 has an ordered structure equal to or less than the wavelength of light, and exhibits optical isotropy when no voltage is applied in the above temperature range, whereby good black display can be performed under crossed Nicols.

  On the other hand, when a voltage is applied between the electrodes 4 and 5 (comb-shaped electrodes) while controlling the temperature of the BABH 8 to 136.7 ° C. or more and 161 ° C. or less using, for example, the heating means described above, cubic symmetry is obtained. Distortion occurs in the structure (ordered structure). That is, the BABH8 is isotropic in the above temperature range when no voltage is applied, and anisotropy is exhibited when a voltage is applied.

  As a result, birefringence occurs in the medium layer 3, so that the display element can perform good white display. Note that the direction in which birefringence occurs is constant, and its magnitude changes with voltage application. The voltage transmittance curve showing the relationship between the voltage applied between the electrodes 4 and 5 (comb electrode) and the transmittance is a temperature range of 136.7 ° C. or higher and 161 ° C. or lower, that is, a wide temperature range of about 20K. Becomes a stable curve. For this reason, when the BABH8 is used as the dielectric medium, temperature control can be performed very easily. That is, since the dielectric medium layer 3 made of BABH8 is a thermally stable phase, it does not exhibit abrupt temperature dependence and is extremely easy to control the temperature.

  In addition, as the dielectric medium, it is possible to realize a system in which liquid crystal molecules are filled with aggregates that are radially aligned with a size equal to or smaller than the wavelength of light and appear optically isotropic. As the method, the liquid crystal microemulsion described in Non-Patent Document 4 and the liquid crystal / fine particle dispersion system described in Non-Patent Document 5 (mixed system in which fine particles are mixed in a solvent (liquid crystal), hereinafter simply referred to as a liquid crystal fine particle dispersion system) It is also possible to apply the method described below. When an electric field is applied to these, a set of radial orientations is distorted, and optical modulation can be induced.

  Any of these liquid crystalline substances may be liquid crystalline as a single substance, or may be liquid crystalline by mixing a plurality of substances. Other non-liquid crystalline substances may be mixed. Furthermore, a polymer / liquid crystal dispersion material as described in Non-Patent Document 1 can also be applied. Further, a gelling agent as described in Non-Patent Document 2 may be added.

  The dielectric medium preferably contains a polar molecule. For example, nitrobenzene or the like is suitable as the dielectric medium. Nitrobenzene is also a type of medium that exhibits the Kerr effect.

  Hereinafter, an example of a substance that can be used as the dielectric medium or a form of the substance is shown, but the present invention is not limited to the following examples.

[Smectic D phase (SmD)]
The smectic D phase (SmD) is one of liquid crystal phases of a liquid crystalline material that can be used as the dielectric medium, has a three-dimensional lattice structure, and has a lattice constant equal to or less than the wavelength of light. For this reason, the smectic D phase is optically isotropic.

  Examples of liquid crystalline substances exhibiting a smectic D phase include the following general formulas (9) and (10) described in Non-Patent Document 3 or Non-Patent Document 8.

ANBC16 represented by the following. In the general formulas (9) and (10), m represents an arbitrary integer, specifically, m = 16 in the general formula (9), m = 15 in the general formula (10), and X Represents a —NO ₂ group.

  The ANBC16 exhibits a smectic D phase in a temperature range of 171.0 ° C. to 197.2 ° C. When an electric field is applied to the ANBC 16 in the above temperature range in which the ANBC 16 exhibits a smectic D phase, the ANBC 16 molecules themselves have dielectric anisotropy, so that the molecules are distorted in the lattice structure as the molecules move in the direction of the electric field. That is, the optical anisotropy appears in ANBC16. Note that the material is not limited to ANBC16, and any material exhibiting a smectic D phase can be applied as a dielectric medium of the display element according to the present embodiment.

[Liquid crystal microemulsion]
A liquid crystal microemulsion is an O / W microemulsion proposed in Non-Patent Document 4 (a system in which water is dissolved in oil in the form of water droplets in an oil, and the oil becomes a continuous phase). A generic term for a system (mixed system) in which oil molecules are replaced with thermotropic liquid crystal molecules.

  Specific examples of the liquid crystal microemulsion include, for example, pentylcyanobiphenyl (5CB), which is a thermotropic liquid crystal exhibiting a nematic liquid crystal phase, and a lyotropic (lyotropic) liquid crystal exhibiting a reverse micelle phase described in Non-Patent Document 4. There is a mixed system with an aqueous solution of didodecyl ammonium bromide (DDAB). This mixed system has a structure represented by schematic views as shown in FIGS.

  In this mixed system, the diameter of reverse micelles is typically about 50 mm, and the distance between the reverse micelles is about 200 mm. These scales are about an order of magnitude smaller than the wavelength of light. In addition, reverse micelles exist randomly in three-dimensional space, and 5CB are radially oriented around each reverse micelle. Therefore, this mixed system is optically isotropic.

  When an electric field is applied to the dielectric medium composed of this mixed system, since the dielectric anisotropy exists in 5CB, the molecule itself tends to face in the electric field direction. That is, orientation anisotropy appears in a system that is optically isotropic because it is oriented radially around a reverse micelle, and optical anisotropy appears. The liquid crystal microemulsion is not limited to the above-described mixed system, and is optically isotropic when no voltage is applied, and exhibits optical anisotropy when voltage is applied. It can be applied as a dielectric medium.

[Lyotropic LCD]
The lyotropic liquid crystal means a liquid crystal of another component system in which the main molecules forming the liquid crystal are dissolved in a solvent having other properties (such as water or an organic solvent). The specific phase is a phase that is optically isotropic when no electric field is applied. Examples of such a specific phase include a micelle phase, a sponge phase, a cubic phase, and a reverse micelle phase described in Non-Patent Document 11. FIG. 5 shows a classification diagram of the lyotropic liquid crystal phase.

  Surfactants that are amphiphilic substances include substances that develop a micelle phase. For example, an aqueous solution of sodium decyl sulfate, which is an ionic surfactant, an aqueous solution of potassium palmitate, and the like form spherical micelles. Further, in a mixed solution of polyoxyethylene nonylphenyl ether, which is a nonionic surfactant, and water, micelles are formed by the nonylphenyl group acting as a hydrophobic group and the oxyethylene chain acting as a hydrophilic group. In addition, micelles are formed even in an aqueous solution of a styrene-ethylene oxide block copolymer.

  For example, spherical micelles exhibit a spherical shape by packing molecules (forming molecular aggregates) in all spatial directions. Further, since the size of the spherical micelle is equal to or less than the wavelength of light, it does not show anisotropy and looks isotropic. However, when an electric field is applied to such spherical micelles, the spherical micelles are distorted, so that anisotropy is expressed. Therefore, the lyotropic liquid crystal having a spherical micelle phase can also be applied as the dielectric medium of the display element according to this embodiment. In addition, the same effect can be acquired even if it uses not only a spherical micelle phase but the micelle phase of another shape, ie, a string-like micelle phase, an elliptical micelle phase, a rod-like micelle phase, etc. as a dielectric medium.

  Further, it is generally known that reverse micelles in which a hydrophilic group and a hydrophobic group are exchanged are formed depending on the conditions of concentration, temperature, and surfactant. Such reverse micelles optically show the same effects as micelles. Therefore, by applying the reverse micelle phase as the dielectric medium, the same effect as that obtained when the micelle phase is used can be obtained. The liquid crystal microemulsion described above is an example of a lyotropic liquid crystal having a reverse micelle phase (reverse micelle structure).

  In addition, the aqueous solution of pentaethylene glycol-dodecyl ether, which is a nonionic surfactant, has a concentration and temperature range showing a sponge phase and a cubic phase as shown in FIG. Such a sponge phase or cubic phase is a transparent substance because it has an order equal to or less than the wavelength of light. That is, a medium composed of these phases is optically isotropic. When a voltage is applied to a medium composed of these phases, the orientation order changes and optical anisotropy appears. Therefore, a lyotropic liquid crystal having a sponge phase or a cubic phase can also be applied as a dielectric medium of the display element according to this embodiment.

[Liquid crystal fine particle dispersion]
The dielectric medium is, for example, a liquid crystal fine particle dispersion in which an aqueous solution of a nonionic surfactant pentaethylene glycol-dodecyl ether is mixed with latex particles whose surface is modified with a sulfate group and having a diameter of about 100 mm. Also good. In the liquid crystal fine particle dispersion system, a sponge phase is developed. However, the dielectric medium used in the present embodiment may be a liquid crystal fine particle dispersion system that expresses the aforementioned micelle phase, cubic phase, reverse micelle phase, or the like. In addition, by using the DDAB in place of the latex particles, an alignment structure similar to the liquid crystal microemulsion described above can be obtained.

[Dendrimer]
A dendrimer is a three-dimensional hyperbranched polymer having a branch for each monomer unit. Since dendrimers have many branches, they have a spherical structure when the molecular weight exceeds a certain level. This spherical structure is a transparent material because it has an order equal to or less than the wavelength of light, and its optical orientation is manifested by changing the orientation order when a voltage is applied. Therefore, the dendrimer can also be applied as a dielectric medium of the display element according to the present embodiment. Further, by using the dendrimer in place of DDAB in the liquid crystal microemulsion described above, an alignment structure similar to that of the liquid crystal microemulsion described above can be obtained. The medium thus obtained can also be applied as the dielectric medium.

[Cholesteric blue phase]
It is known that the cholesteric blue phase has a three-dimensional periodic structure in the helical axis, and the structure has high symmetry (see, for example, Non-Patent Documents 6 and 7). The cholesteric blue phase is an almost transparent substance because it has an order equal to or less than the wavelength of light, and its orientation order is changed by application of a voltage, and optical anisotropy appears. That is, the cholesteric blue phase is optically substantially isotropic, and the liquid crystal molecules tend to move in the electric field direction when an electric field is applied, so that the lattice is distorted and anisotropy is expressed.

  As a substance exhibiting a cholesteric blue phase, for example, “JC1041” (trade name, mixed liquid crystal manufactured by Chisso Corporation) is 48.2% by weight, “5CB” (4-cyano-4′-pentylbiphenyl, nematic liquid crystal). 47.4% by weight and “ZLI-4572” (trade name, a chiral dopant manufactured by Merck & Co., Inc.) at a ratio of 4.4% by weight are known. The composition exhibits a cholesteric blue phase in the temperature range of 330.7K to 331.8K.

[Smectic blue phase]
The smectic blue (BP _Sm ) phase has a highly symmetric structure (for example, see Non-Patent Document 7, Non-Patent Document 10 and the like) and has an order of less than the wavelength of light, as does the costic blue phase. Therefore, it is a substantially transparent substance, and the orientational order is changed by application of voltage, and optical anisotropy is developed. That is, the smectic blue phase is optically substantially isotropic, and the liquid crystal molecules tend to move in the direction of the electric field when an electric field is applied, so that the lattice is distorted and anisotropy is expressed.

In addition, as a substance which shows a smectic blue phase, FH / FH / HH-14BTMHC etc. which are described in the nonpatent literature 10 are mentioned, for example. The material exhibits a BP _Sm 3 phase at 74.4 ° C. to 73.2 ° C., a BP _Sm 2 phase at 73.2 ° C. to 72.3 ° C., and a BP _Sm 1 phase at 72.3 ° C. to 72.1 ° C. . Since the BP _Sm phase has a highly symmetric structure as shown in Non-Patent Document 7, it generally shows optical isotropy. Further, when an electric field is applied to the substance FH / FH / HH-14BTMHC, the lattice is distorted by the liquid crystal molecules moving in the direction of the electric field, and the substance exhibits anisotropy. Therefore, this substance can be used as a dielectric medium of the display element according to this embodiment.

  As described above, the substance that can be used as the dielectric medium in the display element according to the present embodiment is one whose optical anisotropy (refractive index, orientational order) changes even when an electric field is applied. In other words, it may be a substance exhibiting the Pockels effect or the Kerr effect, and may be composed of molecules exhibiting any of a cubic phase, a smectic D phase, a cholesteric blue phase, and a smectic blue phase. A lyotropic liquid crystal or a liquid crystal fine particle dispersion system showing any of a micelle phase, a sponge phase, and a cubic phase may be used. The dielectric medium may be a liquid crystal microemulsion, a dendrimer (dendrimer molecule), an amphiphilic molecule, a copolymer, or a polar molecule other than the above.

  The dielectric medium is not limited to a liquid crystalline substance, and preferably has an ordered structure (orientation order) that is equal to or less than the wavelength of light when a voltage is applied or no voltage is applied. If the ordered structure is less than the wavelength of light, it is optically isotropic. Therefore, by using a dielectric medium whose ordering structure is equal to or less than the wavelength of light when a voltage is applied or when no voltage is applied, the display state when no voltage is applied and when a voltage is applied can be reliably varied.

  Here, the display device described in Patent Document 1 described above is optically anisotropic by applying an electric field using the liquid crystalline materials represented by the structural formulas (1) to (4) as in the present embodiment. The display is performed using the change of sex. Specifically, Patent Document 1 is a display device in which a medium containing a polar molecule in an isotropic phase state (a dielectric medium in this embodiment) is sandwiched between a pair of substrates. However, in the display device described in Patent Document 1, the liquid crystal phase-isotropic phase transition temperature can be lowered, but at the same time, the Kerr constant is lowered, resulting in an increase in driving voltage. It was.

  Therefore, the display element according to the present invention is a display element in which the dielectric medium of the dielectric medium layer 3 includes nonpolar molecules.

  Examples of the nonpolar molecule include n-dodecane as described in Examples below, but in the present embodiment, the nonpolar molecule is not limited to this and may be nonpolar. In addition to dodecane, n-octane, n-decane, and the like can be given. Of these, n-decane is preferred, and n-dodecane is most preferred.

  Furthermore, the content of the nonpolar molecule is not particularly limited, but it can be used in a dielectric medium in the range of 0.5% to 10%, for example.

  By including non-polar molecules in the dielectric medium, the molecular assembly in the dielectric medium is relatively less susceptible to dipolar interactions and the like, and orientation changes are likely to occur. Therefore, an increase in voltage necessary for optical modulation can be suppressed. Therefore, it is possible to realize a display element that prevents the Kerr constant from decreasing and does not have a high liquid crystal phase-isotropic phase transition temperature.

  Next, the display principle in the display element according to this embodiment will be described below. In the following description, a transmissive display element is mainly used as the display element, which is optically isotropic and preferably isotropic when no electric field is applied. The case where a substance exhibiting sex is used will be described as an example, but the present invention is not limited to this.

  First, the principle difference between the display element according to this embodiment and a general liquid crystal display element will be described.

  FIG. 6 is a graph showing the relationship between the applied voltage and the transmittance in the display elements shown in FIGS. 1A and 1B. FIGS. 7A to 7H show optical differences caused by the application of an electric field. The difference in display principle between a display element that uses a change in directionality and a conventional liquid crystal display element is explained by the average refraction of the medium when no voltage is applied (OFF state) and when a voltage is applied (ON state). 7 is a cross-sectional view schematically showing the shape of the index ellipsoid (shown by the shape of the cut surface of the refractive index ellipsoid) and its principal axis direction, and FIGS. A cross-sectional view of a display element that displays using a change in optical anisotropy when no voltage is applied (OFF state), a cross-sectional view of the display element when a voltage is applied (ON state), a TN (Twisted Nematic) method Sectional view when no voltage is applied to the liquid crystal display element of FIG. , A cross-sectional view of a VA (Vertical Alignment) liquid crystal display element when no voltage is applied, a cross-sectional view of the VA liquid crystal display element when a voltage is applied, an IPS (In Plane Switching) liquid crystal display element A cross-sectional view when no voltage is applied, and a cross-sectional view when a voltage is applied to the IPS liquid crystal display element are shown.

In general, the refractive index in a material is not isotropic and varies depending on the direction. This anisotropy of the refractive index is in a direction parallel to the substrate surface (in-plane direction), the opposing direction of the electrodes 4 and 5, the direction perpendicular to the substrate surface (substrate normal direction), and parallel to the substrate surface. An arbitrary orthogonal coordinate system (X ₁ , X ₂ , X ₃ ) is used when the direction (in-plane direction of the substrate) and the direction perpendicular to the opposing direction of both electrodes 4 and 5 are x, y, and z directions, respectively. The following relational expression (1)

(N _ji = n _ij , i, j = 1,2,3)
(Refractive index ellipsoid) (for example, refer nonpatent literature 12). Here, when the above relational expression (1) is rewritten using the coordinate system (Y ₁ , Y ₂ , Y ₃ ) in the principal axis direction of the ellipsoid, the following relational expression (2)

Indicated by n ₁ , n ₂ , n ₃ (hereinafter referred to as nx, ny, nz) are called main refractive indexes, and correspond to half the length of the three main axes in the ellipsoid. Considering a light wave traveling in a direction perpendicular to the Y ₃ = 0 plane from the origin, this light wave has polarization components in the directions of Y ₁ and Y _2, and the refractive indices of the components are nx and ny, respectively. . In general, for light traveling in an arbitrary direction, the plane that passes through the origin and is perpendicular to the traveling direction of the light wave is considered to be the cut surface of the refractive index ellipsoid, and the principal axis direction of this ellipse is the component direction of the polarization of the light wave. Yes, half the length of the main axis corresponds to the refractive index in that direction.

  First, regarding a difference in display principle between a display element that performs display using a change in optical anisotropy due to application of an electric field and a conventional liquid crystal display element, a TN system, a VA system, and an IPS are used as conventional liquid crystal display elements. The method will be described as an example.

  As shown in FIGS. 7C and 7D, in the TN liquid crystal display element, a liquid crystal layer 105 is sandwiched between a pair of substrates 101 and 102 that are arranged to face each other, and the both substrates 101 and 102 are respectively disposed. It has a configuration in which transparent electrodes 103 and 104 (electrodes) are provided. When no voltage is applied, the major axis direction of the liquid crystal molecules in the liquid crystal layer 105 is twisted and aligned, but when a voltage is applied, The major axis direction of the liquid crystal molecules is aligned along the electric field direction. In this case, the average refractive index ellipsoid 105a has a direction in which the principal axis direction (major axis direction) is parallel to the substrate surface (in-plane direction) as shown in FIG. 7C when no voltage is applied. When the direction and voltage are applied, as shown in FIG. 7D, the principal axis direction faces the normal direction of the substrate surface. That is, the shape of the refractive index ellipsoid 105a does not change between when no voltage is applied and when the voltage is applied, and the principal axis direction changes (the refractive index ellipsoid 105a rotates).

  As shown in FIGS. 7E and 7F, the VA liquid crystal display element has a liquid crystal layer 205 sandwiched between a pair of substrates 201 and 202 arranged in opposition to each other. It has a configuration in which transparent electrodes (electrodes) 203 and 204 are provided, and when no voltage is applied, the major axis direction of the liquid crystal molecules in the liquid crystal layer 205 is aligned in a direction substantially perpendicular to the substrate surface. When a voltage is applied, the major axis direction of the liquid crystal molecules is aligned in a direction perpendicular to the electric field. As shown in FIG. 7E, the average refractive index ellipsoid 205a in this case, when no voltage is applied, the principal axis direction (major axis direction) faces the normal direction of the substrate surface, and FIG. As shown in FIG. 5, when a voltage is applied, the principal axis direction is in a direction parallel to the substrate surface (in-plane direction of the substrate). In other words, in the case of a VA liquid crystal display element, as in the case of a TN liquid crystal display element, the shape of the refractive index ellipsoid 205a does not change between when no voltage is applied and when a voltage is applied, and the principal axis direction changes. (Refractive index ellipsoid 205a rotates).

  In addition, as shown in FIGS. 7G and 7H, the IPS liquid crystal display element has a configuration in which a pair of electrodes 302 and 303 are arranged to face each other on the same substrate 301, and is not shown. By applying a voltage to the liquid crystal layer sandwiched between the counter substrate and the electrodes 302 and 303, the alignment direction of the liquid crystal molecules in the liquid crystal layer (the principal axis direction (major axis direction) of the refractive index ellipsoid 305a) ), And different display states can be realized when no voltage is applied and when a voltage is applied. That is, in the case of the IPS mode liquid crystal display element, as in the case of the TN mode and VA mode liquid crystal display elements, when no voltage is applied as shown in FIG. 7G and when a voltage is applied as shown in FIG. The shape of the refractive index ellipsoid 305a does not change, but its principal axis direction changes (the refractive index ellipsoid 305a rotates).

  Thus, in the conventional liquid crystal display element, the liquid crystal molecules are aligned in some direction even when no voltage is applied, and display is performed by changing the alignment direction by applying a voltage (modulation of transmittance). Yes. That is, although the shape of the refractive index ellipsoid does not change, the display is performed by utilizing the fact that the principal axis direction of the refractive index ellipsoid is rotated (changed) by voltage application. That is, in the conventional liquid crystal display element, the degree of alignment order of liquid crystal molecules is constant, and display (modulation of transmittance) is performed by changing the alignment direction.

  On the other hand, a display element that performs display using a change in optical anisotropy due to application of an electric field, including the display element according to the present embodiment, is shown in FIGS. 7A and 7B. The shape of the refractive index ellipsoid 3a when no voltage is applied is spherical, that is, optically isotropic (nx = ny = nz, orientation order = 0), and anisotropy (nx by applying a voltage) > Ny, orientational order> 0). Note that nx, ny, and nz are the main refractive index in the direction parallel to the substrate surface (in-plane direction of the substrate) and the opposing direction of both electrodes 4 and 5, respectively, and the direction perpendicular to the substrate surface (substrate normal direction) ) In the direction parallel to the substrate surface (in-plane direction of the substrate) and perpendicular to the opposing direction of the electrodes 4 and 5.

  The display element according to the present embodiment performs display by modulating the degree of orientation order, for example, with the direction of optical anisotropy being constant (the voltage application direction does not change). The display principle is very different.

  The display element according to this embodiment will be specifically described as follows. FIG. 8 is a diagram related to the display element according to the present embodiment. FIGS. 8A and 8B are both diagrams schematically showing a configuration of the display element according to the present embodiment in a state where no electric field is applied (OFF state), and FIG. 8A is a cross-sectional view. FIG. 8B is a plan view of the main part. FIGS. 8C and 8D are both diagrams schematically showing the configuration of the display element in a voltage application state (ON state), FIG. 8C is a cross-sectional view, and FIG. ) Is a plan view of the main part. 8B and 8D show the configuration of one pixel in the display element, and the illustration of the configuration of the counter substrate 12 is omitted for convenience of explanation. The electrodes 4 and 5 preferably have a continuous wedge structure as shown in FIG.

  As shown in FIGS. 8A and 8B, the display element according to the present embodiment is a dielectric medium sealed between the substrates 1 and 2 when no voltage is applied to the electrodes 4 and 5. Since the (dielectric medium layer 3) exhibits an isotropic phase and is optically isotropic, the display is black.

  On the other hand, as shown in FIGS. 8 (c) and 8 (d), when a voltage is applied to the electrodes 4 and 5, each molecule of the dielectric medium is formed between the electrodes 4 and 5 in the major axis direction. Since it is oriented along the electric field, a birefringence phenomenon appears. Due to this birefringence phenomenon, the transmittance of the display element can be modulated in accordance with the voltage between the electrodes 4 and 5.

  Note that the voltage required to modulate the transmittance of the display element increases at a temperature sufficiently far from the phase transition temperature (transition point), but a voltage of about 0 to 100 V is sufficient at a temperature immediately above the transition point. It is possible to modulate the transmittance.

For example, according to Non-Patent Document 9 and Non-Patent Document 12, if the refractive index in the electric field direction and the refractive index in the direction perpendicular to the electric field direction are n // and n⊥, respectively, the birefringence change (Δn = n // − n⊥) and the external electric field, that is, the electric field E (V / m) is expressed by the following relational expression (3)
Δn = λ · B _k · E ² (3)
It is represented by Here, λ is the wavelength (m) of incident light in vacuum, B _k is the Kerr constant (m / V ² ), and E is the applied electric field strength (V / m).

  The Kerr constant B is known to decrease with a function proportional to 1 / (T-Tni) as the temperature (T) increases, and even if it can be driven with a weak electric field strength near the transition point (Tni). As the temperature (T) rises, the required electric field strength increases rapidly. For this reason, the voltage necessary for modulating the transmittance increases at a temperature sufficiently far from the transition point (a temperature sufficiently higher than the transition point), but at a temperature immediately above the phase transition, the transmission is performed at a voltage of about 100 V or less. The rate can be modulated sufficiently.

  Until now, a substance exhibiting the Kerr effect has a response characteristic of several microseconds to several milliseconds, so that it is expected to be used to make a display by a display device respond to an input voltage at a high speed. The display element using the effect has a problem that the driving voltage is high and the liquid crystal phase-isotropic phase transition temperature is high.

  Therefore, as described above, the display device described in Patent Document 1 can reduce the liquid crystal phase-isotropic phase transition temperature by adding polar molecules such as ethyl alcohol to the liquid crystal material. In addition, the problem that the liquid crystal phase-isotropic phase transition temperature is high could be solved. However, according to the method in the display device described in Patent Document 1, it has become possible to lower the liquid crystal phase-isotropic phase transition temperature, but at the same time reduce the liquid crystal phase-isotropic phase transition temperature. As a result of studies by the inventors of the present application, it has been found that the reduction of the constant causes the drive voltage to increase.

  Therefore, as described above, the display element according to the present invention includes non-polar molecules in the dielectric medium. Nonpolar molecules are less susceptible to effects such as dipole interactions in a molecular assembly in a dielectric medium and are therefore subject to orientation changes. Therefore, an increase in voltage necessary for optical modulation can be suppressed.

  In the present embodiment, as described above, the electrodes 4 and 5 are arranged to face each other on the surface of the one substrate 1 facing the other substrate 2. As described above, the Kerr effect is that the refractive index change Δn of a substance is proportional to the square of the electric field E, and the application direction of the electric field E and the direction of the generated birefringence anisotropy are generally parallel. Therefore, in order to take out this birefringence change Δn as an optical signal, for example, it is necessary to make an optical arrangement in which the application direction of the electric field E and the light traveling direction are orthogonal to each other. In a normal display device, since light passes in a direction perpendicular to the substrate surface, the application direction of the electric field E at this time needs to be parallel to the substrate surface.

  Accordingly, as shown in FIGS. 1 and 2, birefringence anisotropy generated by electric field application is formed by forming electrodes 4 and 5 as electric field application means on the inner surface of at least one of the pair of substrates. Can be easily extracted as a change in the optical signal.

Hereinafter, the present invention will be described in detail based on Examples and Comparative Examples, but the present invention is not limited thereto.
〔Example〕
The following description describes a display element including a nonpolar molecule in a dielectric medium according to the present embodiment. As a [Comparative Example], a display element including a polar molecule in a dielectric medium will be described.

  ITO was used as the electrodes 4 and 5 as the display element having the configuration shown in FIG. Specifically, the electrodes 4 and 5 have a line width of 5 μm, an interelectrode distance of 5 μm, and an electrode thickness of 0.6 μm. As described above, a wedge shape having an angle of less than 90 ° ± 10 ° is formed on the substrate surface. It was set as the electrode which has. A glass substrate was used as the substrate. Further, as the dielectric medium, a mixture in which the structural formulas (5) to (7) shown above were mixed in equal amounts was used, and a mixture obtained by adding 2% of n-dodecane to this mixture was used.

  The layer thickness of the dielectric medium layer 3 (that is, the distance between the substrates 1 and 2) was 10 μm. Further, a polarizing plate was disposed outside both the glass substrates, and an alignment film made of polyimide was formed inside both the glass substrates. The alignment film was previously subjected to a horizontal rubbing treatment.

  The mixture (dielectric medium) was kept at a temperature immediately above the phase transition of the nematic isotropic phase by an external heating device (heating means), and voltage was applied.

[Comparative example]
Next, as a comparative example, a display element including a polar molecule in a dielectric medium was used. That is, as a comparative example, among the display elements having the configuration shown in FIG. 1, a dielectric medium in which 1% of ethyl alcohol is added as a polar molecule to an equivalent mixture of the above structural formulas (5) to (7). Using. For other configurations, those having the same configuration as in the above embodiment were used.

  As in the above example, the mixture (dielectric medium) was kept at a temperature immediately above the phase transition of the nematic isotropic phase by an external heating device (heating means), and voltage was applied.

  For these two types of display elements, the liquid crystal phase-isotropic phase transition temperature and the maximum transmittance were measured. The results are shown in the table below.

  That is, the display device in the above example had an isotropic phase-liquid crystal phase transition temperature of 62 ° C. When a voltage was applied while maintaining the temperature near the isotropic phase-liquid crystal phase transition temperature, the maximum transmittance was obtained at 48V. The display device in the comparative example had an isotropic phase-liquid crystal phase transition temperature of 60 ° C. When a voltage was applied while maintaining the temperature near the isotropic phase-liquid crystal phase transition temperature, the maximum transmittance was obtained at 51V.

  From the above results, it can be seen that the dielectric medium used in the display element according to the present invention has a smaller applied voltage that provides the maximum transmittance than the comparative example. That is, by including nonpolar molecules in the dielectric medium, it is possible to realize a dielectric medium that does not cause a decrease in the Kerr effect and does not have a high liquid crystal phase-isotropic phase transition.

  In the present invention, since the molecules added to the dielectric medium are nonpolar, unlike the comparative example, the packing in the mixed material is relatively unaffected by the influence of dipole interactions and the like, so that it is not so constrained. Therefore, it is considered that the molecular orientation change is more likely to occur and the driving voltage is lowered.

  As described above, it is considered that an increase in voltage necessary for optical modulation can be suppressed by adding nonpolar molecules to the dielectric medium, unlike the comparative example.

  Therefore, the display element according to the present invention can reduce the temperature at which optical modulation is performed while suppressing an increase in the driving voltage even when the Kerr effect exhibiting high-speed response characteristics is used. It was.

  That is, the display device according to the present invention includes a nonpolar molecule in a dielectric medium sandwiched between a pair of substrates, so that the Kerr effect is not lowered even in a display device using the Kerr effect. In addition, it is possible to provide a display element made of a dielectric medium that does not have a high liquid crystal phase-isotropic phase transition.

  Therefore, it is a display element excellent in wide viewing angle characteristics and high-speed response characteristics. For example, an image display device such as a television or a monitor, an OA device such as a word processor or a personal computer, a video camera, a digital camera, a mobile phone, etc. The present invention can be widely applied to image display devices provided in such information terminals. In addition, as described above, the display element of the present invention has a wide viewing angle characteristic and a high-speed response characteristic, and can prevent a decrease in contrast, and thus is suitable for large-screen display and moving image display.

The structure of the electrode in the display element which is one Embodiment of this invention is shown, (a) is a cross section which shows typically schematic structure of the principal part of the display element which concerns on one Embodiment of this invention in a voltage non-application state It is a figure and (b) is sectional drawing which shows typically schematic structure of the principal part of the said display element in a voltage application state. It is a figure which shows the structure of the electrode in the display element of FIG. 1 in one Embodiment of this invention, and also demonstrates the relationship between the polarizing plate absorption axis in the said display element, an electric field (orientation) direction, and a rubbing direction. It is a schematic diagram which shows an example of the reverse micelle phase mixing system of liquid crystal microemulsion. It is a schematic diagram which shows the other example of the reverse micelle phase mixing system of liquid crystal microemulsion. It is a classification diagram of a lyotropic liquid crystal phase. It is a graph which shows the relationship between the applied voltage and the transmittance | permeability in the display element which is one Embodiment of this invention. FIG. 9 shows an embodiment of the present invention, and shows the difference in display principle between a display element that performs display using a change in optical anisotropy due to application of an electric field and a conventional liquid crystal display element when no voltage is applied and It is sectional drawing typically shown in the shape of the average refractive index ellipsoid of a medium at the time of voltage application, and its principal axis direction, (a) is displayed using the change of the optical anisotropy by the application of an electric field. 2 is a cross-sectional view of the display element when voltage is not applied, (b) is a cross-sectional view when voltage is applied to the display element shown in (a), and (c) is no voltage applied to a TN liquid crystal display element. (D) is a cross-sectional view when a voltage is applied to the liquid crystal display element shown in (c), (e) is a cross-sectional view when no voltage is applied to a VA liquid crystal display element, (F) is sectional drawing at the time of the voltage application of the liquid crystal display element shown to (e), (g) is IPS method Is a cross-sectional view of when no voltage is applied to the liquid crystal display device, (h) is a cross-sectional view of when a voltage is applied the liquid crystal display device shown in (g). (A) And (b) is a figure which shows typically schematic structure of the principal part of the display element which concerns on one Embodiment of this invention in a voltage no application state, (c) And (d) is voltage It is a figure which shows typically schematic structure of the principal part of the display element which concerns on one Embodiment of this invention in an application state, (a) and (c) are sectional drawings, (b) and (d) It is a top view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Board | substrate 2 Board | substrate 3 Dielectric medium layer 3a Refractive index ellipsoid 4 Electrode (electric field application means)
4a Comb teeth (wedge type)
5 Electrodes (electric field applying means)
5a Comb teeth (wedge type)
6 Polarizing plate 6a Absorption axis 7 Polarizing plate 7a Absorption axis 8 Electric field 9 Alignment film 10 Alignment film 11 Pixel substrate 12 Counter substrate

Claims (14)

A pair of substrates at least one of which is transparent;
A display element comprising a dielectric medium sandwiched between the pair of substrates and having optical anisotropy changed by application of an electric field,
The display element, wherein the dielectric medium includes nonpolar molecules. An electric field applying means for applying an electric field to the dielectric medium;
The display element according to claim 1, further comprising: a polarizing plate on a side opposite to the surface facing the dielectric medium in at least one of the pair of substrates.   The display element according to claim 1, wherein the dielectric medium exhibits optical isotropy when no electric field is applied, and exhibits optical anisotropy when a voltage is applied.   The display element according to claim 1, wherein the dielectric medium exhibits optical anisotropy when no electric field is applied, and exhibits optical isotropy when a voltage is applied.   2. The display element according to claim 1, wherein the dielectric medium has an alignment order equal to or less than the wavelength of light when a voltage is applied or no voltage is applied.   2. The electric field applying means comprising at least one pair of electrodes for applying an electric field substantially parallel to the substrate surface to the dielectric medium on one of the pair of substrates. The display element as described in.   The display element according to claim 6, wherein the electrode has a wedge shape.   The display element according to claim 7, wherein an angle formed by the wedge-shaped electrode is less than 90 degrees ± 10 degrees.   The display element according to claim 2, wherein an angle formed between an electric field application direction by the electric field application unit and an absorption axis of the polarizing plate is less than 45 degrees ± 10 degrees.   The display element according to claim 1, wherein an alignment film is provided on a surface of at least one of the pair of substrates facing the other substrate.   2. The display element according to claim 1, wherein a surface of at least one of the pair of substrates facing the other substrate is subjected to a horizontal alignment process.   The display element according to claim 10, wherein the alignment film is an organic thin film.   The display element according to claim 10, wherein the alignment film is a polyimide film.   The display element according to claim 1, wherein the dielectric medium includes a liquid crystal substance.

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